In recent years, the importance of the problem of global warming has become increased due to the greenhouse effect of carbon dioxide (CO2) that is a product of combustion of fossil fuel. In the Kyoto Protocol to the United Nations Framework Convention on Climate Change, Japan's goal in reducing the greenroom effect gas emissions is to attain an 8% reduction from the amount of emissions in 1990.
With such a background, studies are energetically made regarding a method of separating and recovering carbon dioxide in a combustion exhaust gas by bringing the combustion exhaust gas and an amine-based absorbing solution into contact with each other, and a method of storing recovered carbon dioxide without releasing carbon dioxide into atmospheric air.
An example of the method of separating and recovering carbon dioxide by using such an absorbing solution includes a step of causing the carbon dioxide in the combustion exhaust gas to be absorbed in the absorbing solution by bringing the combustion exhaust gas and the absorbing solution into contact with each other in an absorption tower, and a step of purging the carbon dioxide from the absorbing solution containing the absorbed carbon dioxide by heating the absorbing solution in a regeneration tower (refer to JP-A 2004-323339 (KOKAI)). The absorbing solution purged of the carbon dioxide is again supplied to the absorption tower to be reused.
JP-A 2002-71647 (KOKAI) discloses an example of a method of measuring a concentration of dissolved carbon dioxide by using ultrasound.